Hard disk drives are used to store large amounts of digital data. In addition to use in connection with general purpose computers, hard disk drives have application in a variety of devices and systems, such as digital video and audio recorders and video game machines. In a typical application, a single power supply is provided for supplying electrical power to the hard disk drive, and to any other devices associated with the apparatus having the power supply. In a typical device interconnected to or including a disk drive, the largest consumer of electrical current is the hard disk drive.
In a contact start stop (CSS) type disk drive, the transducer heads that are used to write information to and read information from the storage disks are suspended above the surfaces of the storage disks by a laminar flow of air created by the spinning of the disks relative to the transducer heads. However, when the disks are not spinning, the transducer heads in such a drive are in contact with the surfaces of the disks. In order to begin spinning the disks from a static state, the stiction between the transducer heads and the surfaces of the disks must first be broken. Breaking this stiction can require providing the spindle motor with an amount of current that is several times greater than the current consumed by the spindle motor and associated disk drive components when the disk drive is in steady state operation (i.e. when the disks have completed spin-up and are rotating at their normal velocity). Accordingly, power supplies used to provide disk drives with operating current have been required to be capable of supplying a relatively large amount of current during start-up of the disk drive, when spin-up of the disks from a static state is required.
In general, spin-up of the disks refers to bringing the disks from a static state to their normal rotational velocity. Start-up of the disk drive refers to bringing the disk drive to a condition in which data may be transferred to or from the disks. Furthermore, the spin-up time refers to the time required to bring the disks from a static state to their normal rotational velocity when read and write operations are conducted. The start-up time refers to the time required to bring the disk drive from a condition in which the disks are stationary to a condition in which read or write operations can be performed. As can be appreciated by one of ordinary skill in the art, the spin-up time may be equal to the start-up time of a disk drive.
More recently, disk drives have been designed with transducer heads that are unloaded from the surfaces of the disks when the disks are stopped or are not spinning quickly enough to create a laminar flow of air sufficient to support the transducer heads over the surfaces of the disks. Such load and unload disk drives therefore remove the need to provide a relatively high start-up current in order to break stiction between the transducer heads and the surfaces of the disks. However, in order to achieve what has been considered to be a reasonably short spin-up time, even such load and unload disk drives have been provided with start-up currents that may be many times greater than the current consumed by a disk drive after spin-up of the disks has been achieved and start-up of the disk drive completed. Furthermore, the current drawn by a conventional disk drive to initiate rotation of the disks is very high because, upon start-up, there is no back electromotive force in the motor used to rotate the disks. Therefore, the start-up current in even a load and unload type disk drive typically establishes the maximum current draw for a particular disk drive.
Systems intended to reduce the power consumed by disk drives during start-up have been proposed. For example, certain systems limit the current supplied to a disk drive upon start-up to a first amount, and if that first amount of current is not successful in rotating the disk, a second, greater amount of current is supplied. Because such systems anticipate supplying increasing amounts of current, they must be provided with power supplies that are capable of reliably supplying those higher amounts of current. Still other devices have attempted to limit start-up current by providing a plurality of windings in the spindle motor. In particular, a relatively large number of windings are used to provide a high start-up torque, and a lesser number of windings are used after higher rotational velocities have been achieved. However, such devices are relatively complicated and expensive to implement. Still other devices limit the current supplied to a disk drive when the current drawn by the disk drive causes the voltage provided by a power supply to drop below a selected amount. However, such an approach results in a disk drive having a variable maximum current draw. Accordingly, existing disk drives have not allowed users to select between a mode that reliably provides a reduced current draw on a power supply, and a mode that provides relatively fast disk spin-up times to achieve relatively fast disk drive start-up times.